These studies will use light scattering to probe the structures responsible for the transparency (and the loss thereof) of ocular tissues, especially the cornea. The approach is to use light scattering measurements to characterize corneas whose physiological conditions have been carefully controlled. Theoretical techniques are used to calculate the scattering expected from model structures and/or from the structures depicted in electron micrographs, and comparisons of the calculated and measured values test the validity of model structures and provide a measure of the influence of fixation procedures on the structures shown in electron micrographs. During the past year we have built and tested a new apparatus with sufficient resolution to measure the depth dependence of scattering in near forward directions, and have examined the effects of transcorneal pressure on the light scattering patterns that are observed when the cornea is placed between crossed polarizers. We have also devised a simple procedure for maintaining a transcorneal pressure while fixing the cornea for electron microscopy. The waviness of the lamallae, seen when the usual fixation procedure is used, is drastically reduced when a pressure is maintained. This result, along with the pressure effect on the polarized light experiment, suggests that the usual light scattering pattern is due to the waviness. During the next year we will make depth dependent measurements of corneal scattering at low angles, investigate the effects of the limiting corneal membranes on the polarized light experiments and calculate the scattering to be expected from wavy lamellae. BIBLIOGRAPHIC REFERENCES: R.A. Farrell and R. L. McCally, "On the Interpretation of Depth Dependent Light Scattering Measurements in Normal Rabbit Corneas" Acta Ophthal., 54, 261-270, 1976. R.L. McCally and R.A. Farrell, "Depth Dependence of Light Scattering from the Normal Rabbit Cornea," Exper. Eye Res. 23, 69-81, 1976.